1. Field of the Invention
The present invention relates to a method for manufacturing a plasma display panel (PDP) having improved firing and/or drying step(s) by forced convection system.
2. Description of Related Art
Conventionally, as an apparatus adopted in a PDP manufacturing method by forced convection system, there is known a flat glass firing oven for firing a dielectric layer, barrier ribs, phosphor layer, and sealing frit formed on a flat glass substrate of the PDP. The dielectric layer, barrier ribs, phosphor layer, and sealing frit are formed by preparing paste or a green sheet containing glass powder and binder resin, and forming the paste or green sheet into a desirable shape to be fired in the firing oven.
As such conventional apparatus for manufacturing the PDP, Japanese Unexamined Patent Publication No. 2002-243368 discloses a continuous firing oven for flat glass substrates shown in FIGS. 8 and 9. In the figures, the conventional continuous firing oven uses a stainless metallic material on its inner surface to have an air-tight structure. The firing oven comprises a plurality of zones in which temperature thereof can be controlled independently of one another. Each zone is connected to a clean air supply pipe 101a and an oven atmosphere exhaust pipe 101b respectively having a damper 116 for controlling air supply amount and a damper 117 for controlling atmosphere exhaust amount. The temperature inside the zones on loading and discharging sides of the firing oven is not more than 250 to 300° C. At least the zones on the loading side respectively have a baffle 107 provided therein for forming an atmosphere circulation path 109. The atmosphere circulation path 109 is provided with a circulation fan 111 and a heating means 110. The baffle 107 has a heat-resistant filter 112 provided at a circulation atmosphere inlet thereof.
As described above, the conventional continuous firing oven for flat glass substrates has the expensive heat-resistant filter 112 provided only in the zones on the loading side of the oven where a large amount of particles are generated from a resin binder. Since the heat-resistant filter is not provided in other zones, the apparatus is made cheaper.
When the heat-resistant filter 112 is provided in the circulation atmosphere inlet of the baffle 107 as described above, flow resistance increases, and thus ability of the circulation fan 111 needs to be enhanced. However, since the heat-resistant filter 112 is not provided in most of the zones, the circulation fan 111 adopted in the continuous firing oven can be cheap. Further, a flat glass substrate 100 is held horizontally and is fed zone by zone through the firing oven, so that the glass substrate 100 does not fall over two adjacent zones. This allows the glass substrate 100 to be uniformly heated in the oven.
The continuous firing oven for flat glass substrates serving as the conventional manufacturing apparatus for a PDP is constructed as described above, so that the heat-resistant filter provided therein removes particles generated by firing the barrier ribs, phosphor layer, dielectric layer, and sealing frit. However, the continuous firing oven has a problem that it can not remove organic component gas (organic gas) generated from binder resin contained in the barrier ribs, phosphor layer, dielectric layer, and sealing frit at the firing thereof. Further, where the organic component is formed into particles of a predetermined size, a filtration rating of the filter needs to be reduced as the particle size becomes smaller. This increases the flow resistance of the heat-resistance filter, and thereby causing an insufficient supply of hot air in the oven.
Where the filtration rating of the filter is increased so as to have a lower flow resistance, fine particles can not be removed. In other words, where a heating system of the oven is the forced convection system, the organic gas containing unremovable fine particles which are separated and discharged from the flat glass substrate 100 is circulated and introduced into the oven again. Thus, a concentration of the organic component contained in the organic gas in the oven does not settle at a specific level and gradually increases. When the concentration of the organic component in the oven becomes higher, the resin binder contained in the constituents of the PDP (dielectric layer, barrier ribs, phosphor layer, sealing frit) decreases in efficiency of firing decomposition (that is, removal of the resin binder becomes incomplete). Consequently, the resin binder or some of its components remain on the substrate even after the firing, resulting in such problems as decrease in transmittance of the dielectric layer and light-emittance of the phosphor layer.
To lower the concentration of the organic component contained in the organic gas in the oven, a method may be used which introduces a large amount of fresh air into the oven continuously. In such a method, however, extra heat energy needs to be supplied in the oven to compensate the amount of the fresh air introduced in the oven, and this results in poor energy efficiency.